Communication devices such as wireless communication devices, that simply may be named wireless devices, may also be known as e.g. User Equipments (UEs), mobile terminals, wireless terminals and/or Mobile Stations (MS). A wireless device is enabled to communicate wirelessly in a wireless communication network that typically is a cellular communications network, which may also be referred to as a wireless communication system, or radio communication system, sometimes also referred to as a cellular radio system, cellular network or cellular communication system. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more Core Networks (CN), comprised within the wireless communication network. The wireless device may further be referred to as a mobile telephone, cellular telephone, laptop, Personal Digital Assistant (PDA), tablet computer, just to mention some further examples. Wireless devices may be so called Machine to Machine (M2M) devices or Machine Type of Communication (MTC) devices, i.e. a device that is not necessarily associated with a conventional user, such as a human, directly using the device.
The wireless device may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.
The cellular communication network covers a geographical area which is divided into cell areas, wherein each cell area is served by at least one base station, or Base Station (BS), e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is typically identified by one or more cell identities. The base station at a base station site provides radio coverage for one or more cells. A cell is thus associated with a geographical area where radio coverage for that cell is provided by the base station at the base station site. Cells may overlap so that several cells cover the same geographical area. By the base station providing or serving a cell is meant that the base station provides radio coverage such that one or more wireless devices located in the geographical area where the radio coverage is provided may be served by the base station in said cell. When a wireless device is said to be served in or by a cell this implies that the wireless device is served by the base station providing radio coverage for the cell. One base station may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the wireless device within range of the base stations.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunication System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communication (originally: Groupe Spécial Mobile).
UMTS is a third generation mobile communication system, which may be referred to as 3rd generation or 3G, and which evolved from the GSM, and provides improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for wireless devices.
General Packet Radio Service (GPRS) is a packet oriented mobile data service on the 2G and 3G cellular communication system's global system for mobile communications (GSM).
Enhanced Data rates for GSM Evolution (EDGE) also known as Enhanced GPRS (EGPRS), or IMT Single Carrier (IMT-SC), or Enhanced Data rates for Global Evolution is a digital mobile phone technology that allows improved data transmission rates as a backward-compatible extension of GSM.
High Speed Packet Access (HSPA) is an amalgamation of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), defined by the 3rd Generation Partnership Project (3GPP), that extends and improves the performance of existing 3rd generation mobile telecommunication networks utilizing the WCDMA. Such networks may be named WCDMA/HSPA.
In 3GPP Long Term Evolution (LTE), which may be referred to as 4th generation or 4G, base stations, which may be referred to as eNodeBs or eNBs, may be directly connected to other base stations and may be directly connected to one or more core networks.
The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies, for example into Evolved UTRAN (E-UTRAN) used in LTE.
The expression downlink, which may be abbreviated DL, is used for the transmission path from the base station to the wireless device. The expression uplink, which may be abbreviated UL, is used for the transmission path in the opposite direction i.e. from the wireless device to the base station.
Machine Type of Communication (MTC) has in recent years, especially in the context of the Internet of Things (IoT), shown to be a growing market segment for cellular technologies, especially for GSM/EDGE with its more or less global coverage, ubiquitous connectivity and price competitive devices. Realization of IoT benefits from utilizing cellular technologies, and GSM technology is of great, perhaps of greatest, interest to utilize, at least initially. In general it is desirable to be able to (re)use existing wireless communication systems and cellular technologies for new type of devices such as MTC devices. An MTC device is typically a wireless device that is a self and/or automatically controlled unattended machine and that is typically not associated with an active human user in order to generate data traffic. A MTC device is typically much more simple, and associated with a more specific application or purpose, than, and in contrast to, a conventional mobile phone or smart phone. MTC involve communication to and/or from MTC devices, which communication typically is of quite different nature and with other requirements than communication associated with e.g. conventional mobile phones and smart phones. In the context of and growth of the IoT, it is evidently so that MTC traffic will be increasing and thus needs to be increasingly supported in and by wireless communication systems.
A problem related to (re)using existing technologies and systems is e.g. that the requirements for the new type of devices typically is different than conventional requirements, e.g. regarding the type and amount of traffic, performance etc. Existing systems have not been developed with these new requirements in mind. Also, traffic generated by new type of devices will typically be in addition to conventional traffic already supported by an existing system, which existing traffic typically needs to continue to be supported by and in the system, preferably without any substantial disturbance and/or deterioration of already supported services and performance.
Any modification need of existing systems and technology should of course be cost efficient, such as enabled by low complexity modifications, and preferably allowing legacy devices already being employed to continue to be used and co-exist with the new type of devices in one and the same wireless communication network.
EC-GSM is e.g. discussed in GP-151039, “New Work Item on Extended Coverage GSM (EC-GSM) for support of Cellular Internet of Things (CIoT_EC_GSM)”, Ericsson LM, Intel, Gemalto N.V., MediaTek Inc., TeliaSonera AB, Sierra Wireless, S.A., Telit Communications S.p.A., ORANGE, Nokia Networks, Alcatel Lucent.
Cellular Internet of Things (IoT), is e.g. discussed in 3GPP TR 45.820 V13.0.0, “Cellular System Support for Ultra Low Complexity and Low Throughput Internet of Things”.
The extended coverage, i.e. a coverage range beyond that of legacy GPRS/EGPRS operation, is in EC-GSM based on blind physical layer repetitions, of e.g. bursts and/or radio blocks, in both uplink and downlink where the number of repetitions is associated to a given Coverage Class (CC). Each CC is approximated with a level of extended coverage range compared to legacy, i.e. conventional, GPRS/EGPRS operation. That is, each CC represents a certain amount of degradation compared to legacy GPRS/EGPRS operation (e.g. 3 dB) such that the number of blind physical layer repetitions associated with each CC is proportional to its corresponding degradation compared to legacy GPRS/EGPRS operation. CC1 typically corresponds to the coverage range of legacy GPRS/EGPRS operation, i.e. extended coverage not used.
The retransmission procedure for the legacy Random Access CHAnnel (RACH) is specified in 3GPP TS 44.018, see e.g. version 12.6.0. In particular the number of slots between two successive RACH messages, excluding the slots containing the messages themselves, is a random value drawn randomly for each new transmission with uniform probability distribution in a set {S, S+1, . . . , S+T 1}, where T is a parameter Tx broadcasted on the Broadcast Control CHannel (BCCH) and the parameter S depends on the Common Control Channel (CCCH) configuration and on the value of Tx-integer as defined in Table 1 below.
TABLE 1Values of parameter SS non combined S combined TX-integerCCCHCCH/SDCCH3, 8, 14, 5055414, 9, 1676525, 10, 20109586, 11, 25163867, 12, 32217115
The CCCH configuration combined Common Control CHannel—(CCCH) and/or Standalone Dedicated Control CHannel (SDCCH) is used for Circuit Switched (CS) services and can thus be disregarded in the analysis. FIG. 1 illustrates the retransmission windows, as dotted rectangles, when the initial RACH request is made on slot 0 in multi frame N. It can be seen that generally the parameters Tx and S controls the size of the window and in which multi frame the re-transmission attempt will occur, respectively. Generally speaking, the parameter S can be used to control if the retransmissions occur in multi frame N+1, N+2, N+3 and N+4, when assuming initial RACH in the first slot in multi frame N.
Generally, the recommendations for the parameter settings are as follows:                If the Access Grant CHannel (AGCH) is not overloaded, the parameter S should be as low as possible in order to shorten access time.        If AGCH is overloaded, the parameter S should be large, e.g. to allow the MS receive an Immediate Assignment.        If RACH collisions are low, then parameter Tx should be low in order to shorten access time)        If RACH collisions are high, the parameter Tx should be large in order to decrease probability for collision at subsequent retransmission attempts.        
To sum it up, the parameters S and T can be tuned to cater for various degrees of RACH and AGCH load. However, whenever the RACH loading increases, then the AGCH loading can be expected to increase in direct proportion. In addition, it should be noted that since the value for the Tx-integer is sent as part of the BCCH, it is not expected to be dynamically adjusted to reflect real time variations in RACH loading. This suggests that operators in practice will simply select a value for the Tx-integer that reflects the spacing of RACH message retransmissions appropriate for the anticipated busy hour loading of any given CCCH, i.e. the greater the busy hour loading anticipated, the greater the value for S that is to be used and the value of the Tx-integer is selected accordingly.
Since RACH transmissions and retransmissions are vital, it is desirable and important that RACH transmissions and retransmission procedures work and are efficient also in the case of EC-GSM.